Debt - Long Term Debt (Phantom) (Detail)	12 Months Ended
	Mar. 31, 2018	Apr. 23, 2015
Senior Unsecured 3.375% Convertible Notes Due 2038
Debt Instrument [Line Items]
Interest rate of debt instrument	3.375%	3.375%
Maturity year	2038
2011 Credit Facility Due 2018
Debt Instrument [Line Items]
Maturity year	2018